One of the most troubling and difficult problems for a technician servicing any electrical circuit is actually locating and resolving intermittent failures. Nowhere is this problem more difficult than in the maintenance of material handling vehicles. By their very nature, such vehicles receive rough treatment as they move over bumpy terrain, turn sharply, or lift and lower large loads. More than any other similar vehicle, material handling vehicles stress their electrical systems to the limit. Potential failures, which usually register "negative" on a static diagnostic survey, are often further advanced when the material handling vehicle is performing in situ operations, thereby registering "positive".
In addition to the above environmental factors which stress the electrical system through shock and vibration, other factors can affect the integrity or consistency of signals within the system. Examples are moisture condensation on contactors or circuits; radio frequency or electromagnetic interference from devices within the vehicle or the warehouse; and metallic materials which distort or otherwise alter the measured electromagnetic fields surrounding a wire which is tracked by a wire-guided truck. This latter example is of particular importance to well-known types of vehicles which are automatically guided along a path defined by a current-carrying wire embedded in the warehouse floor.
Thus, for purposes of this description, the term "intermittent" is meant to include the aforementioned environmental factors, as well as conventional short circuits and the like.
Recently, the material handling industry has developed built-in diagnostic programming for forklift trucks, so that technicians are no longer required to physically examine the internal circuitry of the vehicles. Programmed diagnostic systems now feature a "hands-off" approach to vehicular-system diagnosis. Dashboard displays indicate potential trouble areas in the equipment on a real-time basis. The vehicle operator is alerted to problems through displays and audible tones while operating the vehicle.
Such visible and audible messages, coupled with other information (in the form of operating and maintenance manuals, the experience of the technician himself, etc.), help a technician make decisions of which a program alone may be incapable.
As aforementioned, the chance of intermittency failure, which could be a momentary short circuit, an open circuit or an abnormal signal variation, is usually intensified during operational tasks, when the vehicle systems are beset by shocks and force loadings or other stressful environmental conditions. Such failures can, more often than not, only be assessed during operation of the vehicle. Static diagnostic testing, therefore, is virtually useless in assessing the intermittency failure.
The present invention addresses the problem of diagnosing intermittent failures and operational abnormalities. The current invention has developed a new program and methodology for locating failures and abnormalities occurring during in situ operations.